Meet Lindley Johnson, Planetary Defense Officer (and Asteroid Hunter)

Meet Lindley Johnson, who might have one of the coolest looking business cards out there.

As “Planetary Defense Officer” at NASA headquarters, Lindley Johnson oversees an agency program designed to detect and characterize asteroids that pass near the Earth.

And if an object is found to be on a hazardous trajectory, or could impact the Earth at some point in the future, the planetary defense team figures out what needs to be done next.

Johnson works not only with NASA projects and centers, but also universities and space institutes around the country, as well as international counterparts like the European Space Agency.

In an extended interview with Tech Briefs, which will be featured in next month’s Here’s an Idea™ podcast, Johnson explained how the exciting business of asteroid detection does have its moments that are “like any other office job.”

Here are excerpts from the conversation.

Lindley Johnson

Tech Briefs: Could you characterize the threat of asteroids and hazardous objects to life on Earth?

Lindley Johnson, Planetary Defense Officer, NASA: Although it's an extremely rare event compared to some other natural disasters that we think of, like hurricanes for instance or even volcanoes, it is a reality that an asteroid could strike the Earth. It has happened a lot in the past, and there are still many objects out there that come close to Earth's orbit. So, it could happen again in the future. With velocities that we're talking about – about 17 kilometers a second – the energy releases are equivalent to the detonation of a nuclear weapon.

We just have to change the velocity of the asteroid by a mere fraction of its overall velocity, less than one percent, to cause it to be a miss instead of a hit.

— Lindley Johnson

Tech Briefs: What is considered a “Potentially Hazardous Object?”

Johnson: Near-Earth objects are the ones that we have to look for. Potentially hazardous objects are ones where their orbits bring them into five million miles of Earth's orbit. So, we have to detect these objects and get enough observations to compute their orbits, and compare that orbit out over time to determine how close it may come to the Earth's orbit in the future.

Tech Briefs: How much time do you have between detection and mitigation of an asteroid?

Johnson: Well, it will all depend on the scenario. We sometimes don't detect objects until they've actually had their closest approach to the Earth. That's largely because currently we're using ground-based telescopes to do this. We'd like to be able to get to space-based capabilities.

I would say that you would want to have at least a minimum of five years from detection to impact to have a chance to do something about it. We need to detect an asteroid several years in advance, because even if you had a spacecraft ready to go, it can take two to three years on the outbound journey to get to the asteroid before you can even do anything about it.

Tech Briefs: What is the advantage of space-based detection capabilities?

Johnson: Getting to space allows you to operate in the infrared part of the spectrum, where these objects actually stand out more, because they are radiating the heat they absorb from the Sun. Stars appear much cooler in the infrared. That kind of capability would certainly improve our ability to detect and find this population of potentially hazardous asteroids faster.

Tech Briefs: How much of a coordinated effort is asteroid detection?

Johnson: It’s a very coordinated effort but not highly structured, if you can imagine that. Observatories around the world are detecting and tracking these asteroids. They send their observations to the Minor Planet Center (MPC), which has been established for decades. The observations are then put together there in a catalog containing all the objects that are in the solar system that are smaller than planet-sized. The center determines the orbits and shows observatories when objects are passing close enough to the Earth to be observed.

Tech Briefs: How are astronomer hobbyists helping the effort?

Johnson: There are a number of amateur astronomers around the world that actually are fairly sophisticated in the equipment that provides what we call “follow-up” observations. In other words, after an object has been discovered and the Minor Planet Center puts out the initial orbit, the observers know where to go look. Amateur astronomers can track the orbit and provide observations to MPC that help us to build up our knowledge of the orbit. The more observations we have, the more accurately we can predict that orbit into the future.

Tech Briefs: What are some of the best technologies used to detect asteroids?

Johnson: Well, the whole principle behind being able to do this is being able to cover as wide an area of the sky as you can, as deep as you can. What I mean by “deep” is getting to the dimmest detection limits as possible. These objects are relatively small and quite dim. Some of them are actually very dark objects, almost as dark as a lump of coal. They don't reflect much light and are some of the hardest things to detect in the sky. You need very sensitive devices, but also a device that can cover a wide area of the sky to be able to spot the objects as they move.

More Asteroid Info

Johnson: The charged couple device (CCD) technology is the way almost everybody does [detection] now. Thirty years ago, that wasn't true. Detection was done largely by photography. Astronomers would take a photograph of the sky and come back an hour or two later and take another photograph, and do this even three or four times a night. Then, they’d compare those photographs against each other to detect the movement of the asteroid across the sky.

The large-format CCD cameras are able to cover more of the sky more frequently, and with great sensitivity. It's not just a quick flash like your camera does on your phone. The shutter is open for several seconds, as much as 15 or 20 seconds. Then, with those individual images taken for 15 or 20 seconds, you can image again and again, and stack those images together; the digital processing allows you to eliminate things that are stationary in the image and just focus on something that might be moving across the image.

It's all done with CCD cameras and digital processing of those images to do the comparison across time in an automated manner. The computers can pull out what are the most likely detections, which are then usually looked at by a human, just to do a quality check, before they are sent in to the Minor Planet Center.

Tech Briefs: After a potentially hazardous near-Earth object is detected, what are the next steps? Is there kind of a standard procedure?

Johnson: Potentially hazardous objects are just ones that come within five million miles of the Earth. That doesn't mean that they are an imminent impact by any means. It just means that over the course of time, their orbit could wander in to closer to the Earth and be a true impactor. Those are the ones that we need to keep an eye on.

What we need to do is get enough observations on the object over the course of its orbit to truly understand what that orbit is. With our orbital models, we are able to, with some certainty, project out to about 100 years into the future (if we have sufficient observations on the object) to understand whether it's going to be coming closer to Earth or whether it's going to be moving further away over the course of time.

Tech Briefs: To make these kinds of decisions, what needs to be known about the asteroids themselves?

Johnson: We need to understand their size. Is the object just a small one that the Earth's atmosphere, if it enters, will break it up, and nothing more substantial than small meteorites will reach the ground? Or are the objects large enough that they can withstand those forces as they come through the atmosphere and actually impact on the surface and do some real damage?

Then, we need to be able to understand what those effects might be, based upon the size and also the composition of the objects. Are they just loose balls of sand, so to speak, or are they more substantial rocky material, or even metallic in composition? We need to understand how far they will penetrate into the Earth's atmosphere, and how much the energy release will be if they impact the surface.

Tech Briefs: How can the orbit of an incoming asteroid be disrupted?

Johnson: Just in the last year, we've undertaken a mission called the Double Asteroid Redirection Test. This is to test the kinetic impact technique for changing the orbit of an asteroid.

Most of these deflection efforts operate on the same principle: We just have to change the velocity of the asteroid by a mere fraction of its overall velocity, less than one percent, to cause it to be a miss instead of a hit. Imparting that change in velocity, a few years in advance, will cause its orbit to change over time, and it will be a miss instead of a hit.

The kinetic impactor technique just slams the spacecraft into the asteroid to impart a force change, to change the velocity. But that very fast, or what we call hyper-velocity, impact causes material to blow off the surface of the asteroid. In fact, a crater is made from the ejection of that material, and that actually adds to the overall force of the kinetic impactor.

The Double Asteroid Redirection Test will slam a spacecraft into the moon of an asteroid called Didymos. Didymos is an almost mile-wide asteroid that has a small moon, about the size of a football field, orbiting it. The kinetic impactor will impact Didymos and change the moon's orbit, demonstrating if this technique actually works in the real world.

Radar images of the binary asteroid system Didymos, featuring the main asteroid and its “moonlet.” Didymos is the target for a future NASA mission called the Double Asteroid Redirect Test, or DART. (Image Credit: Aricebo Observatory)

Tech Briefs: Is asteroid mitigation a wide-open field, one with a variety of different ideas?

Johnson: Well, there's certainly all kinds of ideas, and some of them get pretty exotic. You could, for example, just paint one side of the asteroid a whiter color, and the radiation pressure from the reflection of that surface will actually change the orbit of the asteroid over time.

We think the three most reliable techniques, based on studies done by the National Research Council, are the kinetic impactor, which I've just described. Then, there is a technique that's called a Gravity Tractor, where you just station-keep with a spacecraft to the right side of the asteroid to use nature's tug rope gravity, the mutual gravitational attraction of the spacecraft, and the asteroid will slowly move that asteroid off of its original trajectory.

We might even increase that gravitational force by using the spacecraft to go down and grab a large boulder, a several-tens-of-tons boulder, off the surface, and then park that boulder with the spacecraft in that station-keeping position.

Of course, the third technique, which is one that we don't want to have to resort to, is the use of a nuclear explosive device – but not to blow the asteroid up like you see in movies like Armageddon. What would be done would be to detonate the nuclear device above the surface of the asteroid. The explosion irradiation super-heats the regolith, causing material to eject off the surface. That's like giving it a shove by a rocket motor in the other direction.

Tech Briefs: What is a typical day for you?

Johnson: This is a lot like any other office job, but one of the first things I do in the morning is I look at what I call the “catch of the night” – what objects have come in from our sponsored observatories, what has been reported to the Minor Planet Center.

If there was one that the Minor Planet Center found that had possibility of impacting the Earth at some point in the future, I would actually get an automated alert from the Minor Planet Center as soon as they had that data processed. Even if there's a small potential, we would get an alert from both the Minor Planet Center and our Center for NEO Studies out at JPL, which does more precise orbit determination.

The rest of the day can be fairly much like any other program management job here at NASA, overseeing the variety of projects we have. There are some 50 different projects that we have responsibility for here at the Planetary Defense Coordination Office that go from detection and characterization of these objects all the way to coordinating and planning with other agencies.

Tech Briefs: With a job title like “Planetary Defense Officer” and movies like Armageddon, are there any misconceptions that people have of your job and its responsibilities?

Johnson: Well, I think that one of the things that gets misconstrued a lot is that all of this is done in secret – that if we did detect something headed for the Earth that we wouldn't tell anybody about it. When we predict them to pass close to the Earth, any that have any impact probability, even if it's only one in a hundred thousand, appear on the Center for NEO Studies website. That data is all available for folks to see.

In fact, we feel one of our responsibilities is to get the best information that we know out to the public as fast as we can, as well as to our leadership. If something is discovered, we’re probably going to have a race getting the information up and out through our leadership before the Internet starts talking about it.

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